Transmittance ratio spectrometry as a stray radiant energy test method in spectrophotometry

Abstract

This paper attempts to explain the characteristic shape of a transmittance ratio versus reference transmittance curve which was measured with a Unicam SP500 spectrophotometer. A theoretical expression is developed which relates the co-ordinates of the minimum of that curve to the relative stray radiant energy level of the spectrophotometer and to the concentration ratio applicable to the spectrophotometric method in question. The proposed analysis is applied to determine the relative stray radiant energy level in a Perkin-Elmer 551S ratio recording spectrophotometer, operated in both its single-beam and double-beam modes, and the results obtained are compared with that arrived at by applying a more generalised version of the method of Mielenz et al. to the same instrument in both modes.